Generally, a widely known method of imparting electrically non-conductive resin with electrical conductivity uses a resin composition comprising conductive carbon black, carbon fiber, ceramic fiber, or metal fiber. Further, with the aim of reinforcing the strength of the resin, the use of carbon black, carbon fiber, ceramic fiber or metal fiber is preferable. Recently, attempts to realize resin compositions comprising nano-carbon fiber having a diameter of 500 nm or less have been made.
The carbon nanotube was invented in the year 1991 (Nature, 354, 56˜58, 1991), and a method of synthesizing large amounts of carbon nanotubes is disclosed in Japanese Unexamined Patent Publication No. 1994-280116 (laid open on Oct. 4, 1994).
Japanese Unexamined Patent Publication No. 1996-231210 (laid-open on Sep. 10, 1996) discloses a method of separating and purifying carbon nanotubes depending on the difference in molecular weight, size, and electrical conductivity of the carbon nanotubes.
In addition, Japanese Unexamined Patent Publication No. 2004-244490 (laid open on Sep. 2, 2004) discloses a synthetic resin comprising 0.01 wt %˜1 wt % of carbon nanotubes, and also provides a chemical method to increase compatibility between the carbon nanotubes and the resin.
Typically, the carbon nanotube is carbon in a tubular shape, having a diameter ranging from ones to tens of nm, and is classified into a single-walled carbon nanotube, a double-walled carbon nanotube, and a multi-walled carbon nanotube, depending on the number of graphene layers. Further, the electrical properties thereof vary in conjunction with the chirality of the graphene.
However, carbon is present in many various forms, and the properties thereof vary with the structure thereof. For example, in the case of nanofibers, nano-carbon coils having a helical structure with a diameter of a few nm have been reported (Nano Letters, 3, 1299-1304, 2003).
Thus, conventional carbon nanotubes are thoroughly studied with regard to the size of the diameter thereof. Further, with respect to the shape thereof, exemplary are rigid rods or helices. However, the rigid rod is disadvantageous because it is in a liquid crystal state at a specific concentration and thus undesirably undergoes phase separation, and also the strength thereof changes considerably according to its orientation.
Therefore, particles having a bendable shape, that is, a rigid random coil shape, and properties intermediate between those of flexible chain polymers and rigid rod particles, have been considered with the goal of mitigating the above problems. However, research thereon has not yet been conducted.